Influence of sodium environment and load ratio (R) on fatigue crack growth behavior of a type 316 LN stainless steel at 813K

The influence of load ratio (R) on the fatigue crack growth (FCG) behavior of a modified Type 316 LN base material in as-received condition in sodium environment at 813K was evaluated by fitting the combined data at R values of 0.6 and 0.8 to a model equation for three stage fatigue crack growth (FCG) at multiple R-levels. Also, the in-sodium FCG data are compared with the base-line data generated on the same material in air and argon and with the published results on 304 and 316 stainless steel base metals and 16-8-2 weld metal in a liquid sodium environment. In-sodium threshold stress intensity factor range ( Delta K sub th ) dta at R=0.6 and 0.8, corresponded to negligible crack closure which may be attributed to the lower oxygen concentration at the crack tip.